The present invention generally relates to the field of engine fuel control systems which control fuel primarily in accordance with the magnitude of a primary control signal, and more particularly wherein said primary control signal is normally a direct function of sensed engine manifold pressure and is utilized by an engine control microprocessor.
Several prior engine fuel control systems exist in which an electronic engine control microprocessor provides engine fuel injector control signals in accordance with a received primary control signal representative of sensed engine manifold pressure. Typically, these systems cannot properly control engine fuel in the event of a failure of the engine manifold pressure sensor itself or a failure of the primary control signal received by the microprocessor to accurately represent the actual engine manifold pressure. In other words, if either the manifold pressure sensor fails to produce any output signal or if the primary control signal is not directly related to the engine manifold pressure, then the prior engine fuel control systems do not function properly.
Some prior engine fuel control systems have suggested the substitution of a set of expected values of manifold absolute pressure (MAP) in the event of a detected failure of the engine manifold pressure sensor. These prior systems contemplate the substitution of one of two different expected values of engine pressure as a function of the closed throttle switch, wherein this switch merely indicates if the engine throttle is fully closed or not. Such systems have been found to operate unacceptably since in the event of a pressure sensor failure they result in extremely poor engine performance which severely impairs the drivability of automobiles driven by the engine. While the prior art systems therefore prevent a total engine failure in the event of a failure of the engine manifold pressure sensor, the performance of the engine is substantially impaired if the pressure sensor fails.